1. Field of the Invention
The present invention relates to a three-dimensional (3D) MEMS structure and a method of manufacturing the same, and more particularly, to a method of manufacturing a 3D MEMS microstructure capable of forming a floating structure having a step in a simple process without a specific wafer and a 3D MEMS structure manufactured thereby.
2. Discussion of Related Art
Recently, three-dimensional (3D) microelectromechanical system (MEMS) structures have been actively developed. Such 3D MEMS structures are essential in manufacturing various subcompact systems such as an acceleration sensor, a pressure sensor, a microelectromechanical switch or a biosensor.
To use the 3D MEMS structure in mechanical operating and sensing systems, it is essential to manufacture a floating structure that is spaced a predetermined distance from a substrate and freely moves. Further, a sensing electrode or microswitch needs structures having a step in a vertical direction with respect to a substrate.
To manufacture such a MEMS structure having a step, various techniques have been developed. One is a method of manufacturing a microstructure having a step by performing a primary etching process to a predetermined depth through anisotropic etching and patterning using a separate etch mask to perform etching twice. In this case, however, as the step increases, it becomes difficult to perform patterning using an etch mask, and thus the above method is applied only to the case of a lower step. Further, an additional process for forming a step is needed, and after forming the step, a process of forming a floating structure must be performed.
Meanwhile, a method of forming a step by anisotropically etching a substrate vertically using a wafer having a specific crystal orientation and an etching solution has been disclosed. However, this also requires a specific wafer and an etching solution.
FIGS. 1A to 1C illustrate a conventional technique of manufacturing a 3D MEMS structure having a floating structure.
FIG. 1A illustrates a technique using a Si-on-Insulator (SOI) wafer. A floating structure is formed by performing constant anisotropic etching on a lower region of a silicon layer 11 to determine an etch depth with a silicon oxide layer disposed on a substrate 10. However, this technique requires a specific wafer such as an SOI wafer to produce a simple floating structure having no a step.
Meanwhile, FIG. 1B illustrates a technique in which a structure having a predetermined shape is formed on a silicon substrate 20 by anisotropic etching, and a side etching mask 21 is deposited and then isotropic etching is performed to from a floating structure 22. However, according to the above technique, since the floating structure 22 does not have a step, it cannot be applied to manufacturing a MEMS structure requiring vertical operation or detection.
FIG. 1C illustrates a technique using an orientation wafer. Specifically, dry anisotropic etching is performed on an orientation wafer to vertically etch a substrate to a predetermined depth, and wet anisotropic etching is performed on the substrate to be etched in a specific orientation. Thus, upper and lower regions of the structure are selectively etched. According to the above technique, a step can be precisely controlled and structures having multiple steps can be manufactured. However, the technique has disadvantages in that it requires a specific wafer and has lower compatibility with other processes.
Thus, there is an urgent need to develop a method of manufacturing a 3D MEMS structure including a floating structure having a step in a simple process without a specific wafer.